** Description changed: - Currently it's impossible to install from xenial-desktop-amd64.iso on a - wide range of hardware with Nvidia GPUs. + [Description updated to reflect state of 16.04 release ISO] - The problem is invalid opcode(s) when using llvmpipe (the software - opengl fallback, used when using Unity with the Nouveau driver). The - result is that compiz crashes over and over; Upstart will continue to - restart compiz till it gives up. To confirm whether this bug is - happening, switch to a VT and check dmesg, in which you'll see something - like: + == In summary == + + If you have an Intel Skylake (6th gen) CPU and an NVIDIA GPU (or + possibly other GPUs that likewise require use of the llvmpipe opengl + software fallback), a work-around is needed to install Ubuntu 16.04 + desktop. + + To work-around this, you'll need to: + + 1) Choose "Install Ubuntu" in the pre-boot menu (rather than "Try Ubuntu + without installing") + + 2) Check "Download updates while installing Ubuntu" + + ** Note the above work-around wont work till + llvm-toolchain-3.8 1:3.8-2ubuntu3 lands in xenial-updates (it's currently only in xenial-proposed). FIXME: update description once this happens. + + == In detail == + + The Ubuntu 16.04 desktop ISOs includes libllvm3.8 1:3.8-2ubuntu1, which + has a bug that results in invalid JIT code generation when using the + mesa llvmpipe opengl software fallback on Skylake CPUs. + + When you encounter this bug, Unity/Compiz will fail to start, and you'll + see something like this in dmesg: [ 2092.557913] traps: compiz[10155] trap invalid opcode ip:7efc940030d4 sp:7ffccd914ea0 error:0 - A workable solution seems to be to re-build mesa against llvm-3.6-dev, - libclang-3.6-dev (rather that 3.8). This would get us a working Xenial - ISO for the effected hardware. Post 16.04 release, this could be - revisited, and mesa in Xenial could possibly switch back to llvm 3.8 - once this issue is resolved. - - I have mesa test packages built against llvm 3.6 here: - - https://launchpad.net/~jderose/+archive/ubuntu/mesa/+packages - - I couldn't test the installation without a re-spun ISO, but I did - confirm that after updating to the mesa packages in my PPA, I could - again use Unity. So I'm pretty sure this will fix installing from the - ISO as well. - - My hunch is that llvm 3.8 is generating invalid code during its JIT - compilation for llvmpipe, but it could also be the result of memory - corruption. Either way, building mesa against llvm 3.6 seems to be quick - the fix. - - Note this is a regression from 14.04.4 and 15.10, both of which install - fine on the hardware effected by this bug. - - For concrete examples of System76 hardware effected by this: - - 1) All Skylake laptops with 970m, 980m, and 980gtx GPUs - - 2) All Skylake and Haswell-E desktops with 970gtx and 980gtx GPUs - (although strangely, things seem to work with when you connect to a - monitor over HDMI, but always fails when connecting to a monitor over - DisplayPort) - - Note that none of the above failed tested scenarios are using Optimus: - all are using discrete GPU configurations. - - In my testing thus far on the effected hardware, the install always - fails if you choose "Try Ubuntu without installing". The install usually - seems to work when you choose "Install Ubuntu", but even this 2nd - scenario sometimes fails (and when it does, you'll see the same "trap - invalid opcode" bits in dmesg). - - Also note that so far I've only tested amd64, haven't tested i386. - - I suspect there is some deeper weirdness here, but at this point - System76 is just trying to make sure we have a Xenial ISO from which - customers can re-install Ubuntu. - - Old description - =============== - Currently Unity on Xenial is unusable when the llvmpipe software fallback is used, at least on certain hardware. - - For example, from dmesg: - - [ 2092.557913] traps: compiz[10155] trap invalid opcode ip:7efc940030d4 sp:7ffccd914ea0 error:0 - [ 2093.109485] traps: compiz[10192] trap invalid opcode ip:7f38ac01a0d4 sp:7ffe5ed737e0 error:0 - [ 2093.718863] traps: compiz[10212] trap invalid opcode ip:7fe6900010d4 sp:7ffd55804020 error:0 - - This definitely effects hardware we've tested with NVIDIA 970m and 980m - GPUs (when using the nouveau driver), and probably effects others as - well. - - Although strangely, with some NVIDIA 900 series hardware we're not - seeing this bug when using the nouveau driver. This will be investigated - further. - - In the current state, it's not possible to install Xenial on effected - hardware using recent daily desktop amd64 ISOs. - - Note this problem exists both when run against mesa 11.1.2-1ubuntu2 in - Xenial proper, and when run against mesa 11.2.0~rc4-1ubuntu0.1 from - ppa:canonical-x/x-staging. (The later test was done with the System76 - imaging system using an image with ppa:canonical-x/x-staging and - nvidia-361 pre-installed, then removing nvidia-361 and rebooting). - - I'm kinda shooting in the dark here, but I did my best to rule out the - kernel as a variable: - - (1) I built and installed the 4.4.0-16 kernel on 15.10, rebooted, and - had no problems. - - (2) On Xenial I tried the 4.5 and 4.6rc1 mainline builds, but they don't - fix the problem. - - I'm not sure the underling bug is in compiz, but I'm filing it against - compiz anyway because that's where the dmesg output is pointing me. - - Other likely culprits include nux, mesa, maybe even llvm, and probably - others I'm not thinking of :) - - Also, I'm positive llvmpipe is being used when this invalid opcode is - trapped because I added this to - /etc/X11/Xsession.d/50_check_unity_support: - - /usr/lib/nux/unity_support_test -p > /tmp/compiz-debug.log - - That way I could figure out what renderer was being used from a VT (as - the X session is darn near unusable in this state). + libllvm3.8 1:3.8-2ubuntu3 fixes this issue, but the fix did not make it + onto the 16.04 release ISO. It will be included on the 16.04.1 ISO.
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1564156 Title: xenial: invalid opcode when using llvmpipe To manage notifications about this bug go to: https://bugs.launchpad.net/oem-priority/+bug/1564156/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
